The materials used in the manufacture of IR lenses (e.g., monocrystalline Germanium) are generally expensive relative to materials used in the manufacture of lens for visible or near-visible light, and the cost of IR lenses tends to scale with the cube of their linear size. As a result, IR sensors are made small to reduce the cost to a practical level. Thus one needs small, highly accurate thermal sensors. There are only a few materials and techniques able to give good room-temperature thermal performance in a pixel of the scale of thermal wavelength (about 10 μm) on a side. High-quality vacuum-sealed thermal transducers are the current industry standard because they offer adequate performance at the appropriate size. However, such transducers are prohibitively expensive for many applications.
IR image sensors sensitive to wavelengths in a range such as 3 to 30 microns generally produce images that are of low resolution relative to those that sense visible or near-visible light in a range such as 300 to 1200 nm. In this context, high and low-resolution refer to information content, not necessarily the number of pixels in an image. A very blurry infrared energy image sampled by a microbolometer or thermopile sensor array comprising a large number of pixels may nevertheless be considered “low-resolution” because of the optics and thermal properties of the scene and the response functions of the sensing pixels. Whatever the pixel count, infrared images may be ineffective for providing viewers with sufficient information, such as image details for tasks such as accurately counting objects, animals, or people.